how to refer to a previous value in longitudinal data set

I am working with a longitudinal data; students received a degree at a certain time; I wonder how I can change all the values to 1 after degree attainment. For example, this is what my data looks like now:

Id time award

1 1 .

1 2 .

1 3 1

1 4 .

1 5 .

What I would like to do is to change the two missing values for time=5 and time=6 into 1. Any help is appreciated~!